The major objective of the Proposed Research Studies are to continue to determine the ways in which whole body protein and amino acid metabolism in human subjects responds to changes in dietary protein, amino acid and energy intakes. The long-lerm objective is to provide an understanding of the adaptive nature of human protein metabolism in order to develop better measures of protein nutritional status and more rational approaches for establishing nutrient requirements. The studies will involve the use of new methods for determining rates of whole body protein synthesis and breakdown and for exploring the fate of individuals essential amino acids in healthy adults, explored with the acid of amino acids labeled with non-radio active, stabe isotopes (15N and 13C). The continuous infusion technique is chosen for this purpose.